A thin-film capacitor of which a dielectric layer and internal electrodes sandwiching the dielectric layer are formed through a thin-film process is typically small in size and has a low equivalent series inductance (ESL). Thus, such a capacitor is used in a filter in a high-frequency circuit or used in a matching circuit.
A conventional thin-film capacitor has a structure in which a (BaxSr1-x)TiO3 film (hereinafter, referred to as a BST film) having a high dielectric constant is sandwiched by an upper electrode and a lower electrode, as indicated in Patent Document 1, for example.
A BST film is fired at a high temperature of approximately no lower than 800° C. nor higher than 1000° C. in an oxidizing atmosphere. Thus, a platinum (Pt) thin film formed through sputtering is used for an internal electrode. Although tungsten (W) also meets the firing condition described above, tungsten has a low electrical conductivity and is thus not suitable from the viewpoint of low ESR performance.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2010-21234